This invention relates to a miniature, direct-drive robotic apparatus, and more particularly to a substantially-balanced, multi-axis, direct-drive mini-robot capable of repeatable movements at micron precision.
Miniature robots are smaller, low-mass robotic devices often having finer precision or smaller work-spaces than large-scale robotic devices. Mini-robots are desirable for space, medical and other applications. In space, economic and other pressures are shifting emphasis from heavy, high-cost complex robotic systems to low-mass, low-cost systems providing fewer functions. In medicine, similar economic pressures are encouraging substitution of traditional surgical operations with less invasive endoscopic operations using miniature robotic devices. An advantage of robotic devices for many applications is that humans can be located away from physical risk. In space humans can avoid the vacuum of space. In medicine humans can avoid proximity to infectious diseases.
Among the many applications contemplated for a mini-robot such as described herein are cell penetration, sample handling, micro-manipulation with scaled force reflection, and tele-operation functions. Cell penetration is useful for membrane potential sensing, voltage clamping, dye injection, micro-injection and genetic engineering. Sample handling is useful for handling sub-micro-liter liquid samples in electrophoresis applications. Micro-manipulation movement having scaled force reflection is useful in various clean room manufacturing processes. Tele-operation is useful for space and other remote applications.
Direct drive of a robot is accomplished with an actuator directly coupled to a load. Mechanical gearing and other transmission elements between the actuator and load are substantially eliminated. To achieve low mass mini-robot devices, mini-actuators are needed. Suitable mini-actuators are found in the computer disk drive industry for 5.25", 3.5" and 2.5" disk drives. Desire for miniaturization in such field is likely to lead to smaller mini-actuators which can be used for mini-robots.
One of the challenges in designing robotic devices and mini-robotic devices is to provide repeatable movements at a desired precision. Effects of inertia, non-linear control responses and friction often hinder repeatable performance. Accordingly, there is a need for a mini-robot capable of repeatable micro-manipulation at micron precision within desired response times.
A three-axis direct-drive mini-robot is described by co-inventors Hannaford and Marbot in "Mini Direct Drive Robot Arm for Biomedical Application;" IEEE, 1991. The robot therein has three closed loop degrees of freedom and one open loop piezo-electric device. Closed loop tip positioning accuracy is to 20 microns, and open loop incremental positioning accuracy is to 1 micron. A work space of approximately 17 cc is available. Herein, co-inventors, Hannaford, Marbot and Moreyra have improved the mini-robot by adding two degrees of freedom and increasing the work space, while limiting inertia effects and other adverse dynamic effects. The five-axis direct drive mini-robot of this invention provides repeatable micro-movements with more dexterous motion and improved precision.